1. Field of the Invention
This invention relates generally to a method of forming a cast-in-place concrete pile and particularly to a method of demolishing or removing an upper end of such a concrete pile.
2. Prior Art
In the construction of structures such as a building and a bridge, cast-in-place concrete piles have been extensively used for building foundations. The cast-in-place concrete pile is formed by boring a hole in the ground and pouring concrete into the hole. Such a hole is, for example, formed using an earth auger. Usually, a suitable liquid such as a bentonite solution is filled in the hole to prevent the wall of the hole from crumbling, and a shell or tube of a thin steel sheet is fitted in the hole. Then, a reinforcement of a latticework is inserted into the hole, and concrete is poured into the hole through a tremie pipe to replace the above-mentioned liquid, thereby casting a concrete pile. The shell is then withdrawn from the ground. Finally, the upper portion of the cast concrete pile is removed or demolished by a suitable demolition means such as a hammer to provide the finish concrete pile of a predetermined height.
The upper portion of the cast concrete pile is removed because the upper portion has a poor quality. More specifically, a small amount of soil or the like is deposited on the bottom of the hole in which the liquid such as a bentonite solution is filled. When concrete is poured into the hole through the tremie pipe, the soil deposited on the bottom of the hole is moved upwardly so that the upper portion of the resultant concrete pile contains the soil and the liquid as impurities. Therefore, the upper portion of such a concrete pile has failed to have a sufficient strength for the building foundation, and such a concrete pile could not be satisfactorily jointed to a footing of the building. Therefore, the upper portion of the cured concrete pile having a poor quality has heretofore been removed or demolished by the use of a breaker or the like after the withdrawal of the shell and the excavation of the ground around the pile. This method has been found disadvantageous, however, from a viewpoint of environmental pollution, since it gives rise to substantial noises and vibrations. In addition, this method has required relatively much time and labor. In order to overcome such difficulties, the use of an expansive demolition-facilitating substance has been recently proposed to efficiently demolish the upper portion of the cast concrete pile. With this method, the upper portion of the concrete pile can be demolished easily in a quiet manner. This conventional method will now be described in more detail with reference to FIGS. 1 and 2.
U-shaped and straight hollow spiral sheathed tubes 11 and 12 are mounted within a shell 13 at its upper portion above a predetermined plane 14 of demolition, the shell 13 being placed in a hole in the ground. The upper portion 15 of the cast concrete pile 16 above the demolition plane 14 is to be removed or demolished. Concrete is poured into the shell 13 beyond the demolition plane to cover the hollow tubes 11 and 12. Then, the shell 13 is withdrawn from the ground, and the ground around the cast concrete pile 16 is subjected to excavation. Then, an expansive demolition-facilitating substance, for example, one manufactured and sold by Sumitomo Semento Kabushiki Kaisha (Japan) under the tradename of S-mite, is filled in the hollow tubes 11 and 12. The demolition-facilitating substance in the hollow tubes 11 and 12 is expanded upon the lapse of a predetermined time so that it ruptures the hollow tubes 11 and 12 and causes cracks in the upper portion 15 of the cast concrete pile 16 to demolish it. The hollow tubes 11 and 12 have such a nature that they will not prevent the expansion of the demolition-facilitating substance.
In this demolishing method, it is important that the concrete pile 16 should not be subjected to demolition or damage below the demolition plane 14. Therefore, the U-shaped hollow tubes 11 and the straight hollow tubes 12 are so arranged that the concrete pile 16 is not subjected to such damage. More specifically, the U-shaped hollow tubes 11 each defined by a pair of arms 11a and 11a and a base 11b interconnecting the arms are arranged in parallel spaced relation with their respective arms 11a disposed vertically adjacent to the inner peripheral surface of the shell 13, their bases 11b being disposed horizontally and spaced upwardly from the demolition plane 14 a predetermined distance. One or more of the straight hollow tubes 12 are vertically disposed between the arms 11a and 11a of each of the U-shaped hollow tubes 11. With this arrangement, the arms 11a of the U-shaped hollow tubes 11 and the vertical straight hollow tubes 12 both containing the demolition-facilitating substance serve to produce vertical cracks in the upper end 15 of the concrete pile while the horizontal bases 11b of the U-shaped hollow tubes 11 containing the demolition-facilitating substance serve to produce horizontal cracks in the upper end 15 of the concrete pile 16.
The base 11b of each U-shaped hollow tube 11 can be first filled with the demolition-facilitating substance, and later the arms 11a can be filled with this substance. Therefore, the horizontal cracks are first produced in the upper portion 15 of the concrete pile 16, and then the vertical cracks are produced therein. This procedure ensures that the concrete pile 16 is not subjected to cracks below the demolition plane 14.
This conventional method has been found disadvantageous, however, in that the installation of the concrete pile 16 requires much time since the demolition-facilitating substance is filled in the hollow tubes 11 and 12 after the concrete is cured. In addition, the filling of the demolition-facilitating substance into the horizontal bases 11b of the U-shaped hollow tubes 11 and the filling of this substance into the vertical arms 11a and the vertical straight hollow tubes 12 are carried out separately at different stages. This aggravates the problem of the installation time. Further, since the demolition-facilitating substance is applied to the hollow tubes 11 and 12 after the concrete pile 16 has been cured, foreign matters such as muddy water tend to be introduced into the hollow tubes 11 and 12 during the curing of the concrete. As a result, it is possible that the upper portion 15 of the concrete pile 16 is not demolished satisfactorily. Further, there is a possibility that the hollow tubes 11 and 12 and reinforcement bars are subjected to damage when excavating the ground around the concrete pile 16, so that the demolition-facilitating substance is not filled in the hollow tubes 11 and 12 satisfactorily.